The invention concerns a safety switch for a rotatably driven milking carousel.
A generic milking carousel is known for example from FIG. 5 of WO 2004/23866, as well as from patent applications parallel to this publication and going back to the same priority.
In rotary milking parlors, there is a central rotating platform with milking stalls where dairy animals are milked, and a stationary platform that partially surrounds the rotating platform. The stationary platform includes an animal passageway through which animals enter and egress the rotary platform while it is rotating. This portion of the stationary platform is also called an animal bridge. The stationary platform is situated close to the rotary platform so that the animals can step safely over a narrow gap and onto the rotary platform and back again after milking. Dairy workers must stand in a relatively wide area next to the rotary platform to prepare animals for milking. Between the wide worker area and the narrow gap between the animal bridge and the rotary platform is a transition region that narrows down. The transition region is a critical location because after a milking process, a milking machine is let down into a lowered position to hang outside the peripheral edge of the rotary milking platform The milking machine hangs from a rope or chain and the milking machine includes hoses that must pass into the gap without becoming stuck. Moreover, this region is naturally sensitive from the point of view of safety technology because milker operators, who spend time near the milking platform, must be careful that their bodies and extremities are not pulled inadvertently into the gap between the rotating milking platform and the animal passage.
To solve this problem area of safety technology, different safety devices have already been developed. Thus, it is known that a safety switch designed as an emergency cut-off switch can be arranged in the critical transition region with which the movement of the milking carousel can be stopped.
A known safety switching device has two safety switches that are positioned at suitable locations before the gap, and which react to contact, for example by a bulky milking machine that rotates with the milking platform. This contact shuts down the rotary platform.
In another known solution, the first of the two safety switches is arranged in a stationary manner in the direction of rotation at such a distance from the animal bridge that it can be triggered by an excessively bulky milking machine, which again initiates stoppage of the milking carousel to protect the machine. Nonetheless, due to the inertia, the milking carousel continues to rotate by a certain angle or path before it stops. Consequently, the distance between the switch and the gap should be large enough that the rotary milking platform always comes to a stop before the milking machine can be pulled into the gap between the animal bridge and the milking platform.
In spite of this, in practice, there is a problem because several milker operators work at the carousel. Specifically, it happens that the milker operator, who is at the milking carousel and nearest the stationary animal passageway and the animal access to the carousel, restarts the carousel after it had been stopped by the first safety switch without having eliminated the cause of the triggering of the first safety switch. This occurs regularly since the bulky milking machine will go past the first switch due to the inertia of the carousel and the milker operator cannot see the area of the first and second safety switch from his position. After the milker operator has restarted the carousel, the bulky milking machine will activate the second safety switch that is significantly closer to the stationary animal passage gap. The carousel stops again, but, due to the inertia of the carousel, the bulky milking machine comes into the gap between the outer periphery of the milking carousel and the stationary animal passageway, so that the milking machine is destroyed.
Moreover, it is disadvantageous that the existing two safety switches stop the carousel when corresponding sensors come into contact with water and excrement, which causes to false alarms.
This relatively expensive solution should be simplified constructively and with regard to its safety function. The solution to this problem is the task of the invention.